1. Field of the invention
The present invention generally relates to a camera having a photographing optical system and a view finder optical system separately and more particularly to a view finder comprising a means for compensating parallax and gap in diopter possibly occurring in the view finder optical system at the time of macro-photographing.
2. Description of the related art
Hitherto, cameras except those of the single-lens reflex type are generally constituted with an optical axis for the view finder optical system separate from that for the photographing optical system. Hence, the light directed to a camera from a given point on the optical axis for the photographing optical system forms an image on the optical axis for the photographing optical system, while in the view finder optical system the image is formed at a position off its optical axis. The extent of the gap between the position of image formation and the optical axis for the view finder optical system, namely the parallax, is almost small enough not to cause any problem when the aforementioned given point is extremely far from the image-forming plane but it increases progressively with decreasing distance therebetween and accordingly the gap between the center of the taking scope and the center of the view finder's field of view increases gradually but progressively. Especially, in case of macro-photographing, if the frame of the visual field to be used is the same as that at the time of normal photographing, the picture in the view finder is different from the picture actually taken.
An arrangement for solving such a problem is or known one in which, as shown in FIG. 1A and FIG. 1B, the view finder has marked therein a frame showing the field of vision, i.e. visual field frame 50A or 50B for macro-photographing in addition to the visual field frame 50 for normal photographing. Even in this case, it is extremely difficult to see the four corners of the visual field frame for macro-photographing, i.e. the precise taking scope. Also, if, for instance, the photographer has scarcely any interest in a camera, it is even possible that photographing is done without knowing that in macro-photographing the taking scope is to be matched with the visual field frame for macrophotographing.
As another arrangement for compensation of parallax, it is possible to add an optical element to the view finder optical system. As to such an arrangement, the techniques involved are disclosed in Japanese Laid-Open Patent Publication 62-284336, Laid-Open Patent Publication 62-52114, Laid-Open Utility Model Publication 63-70539 et cetera, but these are all based on the principle of disposing a prism on the object lens side of the view finder optical system and compensating the parallax by utilizing the refraction of light by this prism.
Meanwhile, since, in the case of a single-lens reflex camera, it is so arranged that the focused image condition is formed always on the image-forming plane regardless of the object distance, the object's image can be seen at the same position also in the view finder. Hence, since the distance between the photographer's eye and the image-forming position is kept constant, the diopter or the distance at which the object's image is visible to the photographer is always constant. In a camera with the photographing optical system and the view finder optical system provided separately as described above, it is a usual practice not to vary the view finder optical system according to the object distance, hence the image-forming position varies with the object distance. The diopter, too, varies accordingly, hence especially when the variation of diopter as in the case of macro-photographing, no focused image is visible in the view finder.
The term gap in diopters refers to the difference in image plane caused by the difference in object distance. Diopter is the distance at which the object image is visible to the photographer. Basically, a gap in diopters will be the displacement of the image of the object behind the desired predetermined plane in the viewfinder optical system. As a result, a formed image can be blurred to the photographer, since the eyepiece is generally located at an appropriate position wherein the object image formed at the predetermined plane appears most clearly to the photographer. When an object is at an infinite distance, any gap in diopters or change in diopters will not present a problem. However, when a viewfinder optical system is utilized in macrophotography, both parallax and a gap in diopters can present problems.
Hence, in macro-photographing it is necessary to compensate the gap in diopter together with the parallax for the photographer to be able to see a proper image in the view finder. It is, however, not desirable to compensate them by different means for it inevitably results in complication of the compensating mechanism, which, in turn, results in enlargement of the view finder.